The invention relates to a drill bit, and more specifically, to a cylindrical bit with hard metal cutting edges. Such a cylindrical bit is a drilling tool which has a disc-like, that is a cylindrical, head provided at its front side and, possibly at its circumference, with a number of cutting edges.
Such drill bits consist usually of a tool body of tool steel which includes a head into which cutting edges of hard metal are inserted or onto which the cutting edges are soldered or welded. The manufacturing process for such drill bits with individually manufactured and installed cutting edges however is time-consuming and expensive.
The alternative possibility to make the tool completely from hard metal is not desirable either since such hard metal is very expensive, whereby the tool would become even more expensive.
It is therefore the object of the present invention to provide an improved design of a cylindrical bit, which is easier and less expensive to manufacture.
In a cylindrical drill bit comprising a tool body with a head having a front face and a cylindrical shaft for chucking the tool body, a hard metal cutting plate structure is mounted on the front face of the head and includes cutting edges formed integrally with the hard metal cutting plate.
The drill bit according to the invention consists accordingly of a body of a tool steel with a head formed by a simple disc having a flat front face. On the front surface, a cutting plate is disposed which consists completely of hard metal and which is attached to the front face by soldering or cementing. This hard metal plate is in the form of a spoke wheel that is it does not have the form of a flat disc, but it is provided with openings whereby a substantial amount of hard metal is saved. The cutting plate may be manufactured by injection molding from a hard metal powder which is mixed with a medium that makes it flowable so that it can be molded by injection molding, as is known per se. The cutting plate is therefore molded in essentially its final shape that is with cutting edge structures which later only need to be ground to form the cutting edges.
The front surface of the tool body may be provided with fitting pins, which in co-operation with the openings in the cutting plate provide for a centering of the cutting plate on the tool body head when placed thereon.
An embodiment of the invention will be described in greater detail below on the basis of the accompanying drawings.